Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-05-15
Astron.Astrophys.472:L13-L16,2007
Astronomy and Astrophysics
Astrophysics
4 pages, 3 figures. Accepted for publication in A&A Letters
Scientific paper
10.1051/0004-6361:20077799
This Letter reports on the photometric detection of transits of the Neptune-mass planet orbiting the nearby M-dwarf star GJ 436. It is by far the closest, smallest and least massive transiting planet detected so far. Its mass is slightly larger than Neptune's at M = 22.6 +- 1.9 M_earth. The shape and depth of the transit lightcurves show that it is crossing the host star disc near its limb (impact parameter 0.84 +- 0.03) and that the planet size is comparable to that of Uranus and Neptune, R = 25200 +- 2200 km = 3.95 +- 0.35 R_earth. Its main constituant is therefore very likely to be water ice. If the current planet structure models are correct, an outer layer of H/He constituting up to ten percent in mass is probably needed on top of the ice to account for the observed radius.
Demory Brice-Olivier
Gillon Michael
Mallmann F.
Mayor Marcel
Mazeh Tsevi
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